At present, from the viewpoint of conservation of the global environment, such technique is desired which can efficiently utilize the energy that used to be wasted. In particular, a technique that can convert wasted energy into mechanical energy is desired. For example, a Rankine bottoming cycle which generates steam to rotate a turbine, a Sterling cycle system using waste heat, a thermoelectric conversion system using a thermoelectric conversion element part, and a thermoacoustic system converting thermal energy into acoustic energy are known.
The thermoacoustic system uses a thermoacoustic conversion technique for exchanging energy between acoustic energy (sound pressure energy) and thermal energy. The system uses a compression process and an expansion process in a fluid element of a fluid in which acoustic waves travel. Specifically, the technique uses the behavior of the compression process and the expansion process in the fluid element taking place at different locations (along the traveling direction of acoustic waves) for longitudinal oscillations (acoustic waves).
Example thermoacoustic systems using the thermoacoustic conversion technique include a system with an apparatus having a sufficient contact area between a solid part and gas, where one end of the solid part is heated and a portion of heat is converted into acoustic energy which is supplied to the electric power generator. The key feature of the system is the temperature gradient in the solid part of the apparatus, though the efficiency of converting energy into acoustic wave energy is disadvantageously low. The disadvantage is due to an undesirable structure and property of the thermoacoustic energy converting element part configured to convert thermal energy into sound pressure energy.
As an example of the thermoacoustic energy converting element part used in the thermoacoustic system, a thermoacoustic stack is known that is made compact to generate self-excited oscillation even with high frequency under low temperature difference (JP 2012-237295A).
The thermoacoustic stack includes a plurality of through holes and is made of a material having thermal conductivity lower than 10 W/m·K. For a shorter stack length, the temperature gradient can be scaled down (proportionally reduced) so that the temperature at a high temperature side heat exchanging unit, which is required to generate a critical temperature gradient, can be reduced.
By using the aforementioned stack, the required temperature for the high temperature side heat exchanging unit to achieve the critical temperature gradient can efficiently be reduced. At present, however, the efficiency of energy conversion between acoustic waves and heat is still low.
An object of the present invention is to provide a thermoacoustic energy converting element part that can efficiently convert acoustic energy to thermal energy or thermal energy to acoustic energy between the fluid, through which acoustic waves travel, and a wall in contact with the fluid, a thermoacoustic energy converter, and a method of manufacturing a thermoacoustic energy converting element part.